Conventionally, in a copying machine, a printer, a facsimile, or other image forming apparatus of the electro-photographic printing system, a toner image is formed by developing an electrostatic latent image formed on an image holding member (photoreceptor), and further transferring the toner image formed onto a sheet to be affixed thereto, thereby forming an image on a sheet. For this image holding member, generally adopted is a photoreceptor drum whose peripheral surface is coated with a photosensitive film.
By the way, in order to obtain a desirable image using the foregoing photoreceptor drum, it is required to exchange the photoreceptor drum periodically. In response, the photoreceptor drum is stored in an exchangeable unit structure to be detachable from an image forming apparatus main body with ease. The photoreceptor drum becomes rotatable upon receiving rotation-driving force from a rotation drive section of the image forming apparatus main body. As means for transmitting the rotation driving force from the image forming apparatus main body, for example, as disclosed in Japanese Patent Publication No. 64-21466/1989 (Tokukaisho 64-21466, published on Jan. 24, 1989), generally adopted is gear transmission means, or coupling means (relay means) wherein a recessed part and a protruded part respectively formed on a drive section and a driven section are in engagement.
On the other hand, in order to obtain a desirable image using the photoreceptor drum, it is necessary to apply uniform rotation driving forces to the photoreceptor drum. Here, generation of jerky movement of the driving force transmission means for transmitting the driving force to the photoreceptor drum would be the problem.
In order to prevent such jerky rotation movement, the gear transmission means of Japanese Patent Publication No. 64-21466/1989 is arranged so as to provide an internal gear with a taper provided at a flange having attached thereto a photoreceptor drum and an external gear provided with a taper on a side of a drive section. As a result, the jerky rotation movement to be transmitted from the driving force transmission means to the photoreceptor drum can be suppressed.
Japanese Patent No. 3078464 (U.S. Pat. No. 6,188,857; U.S. Pat. No. 6,161,446; and U.S. Pat. No. 5,927,148) discloses a photoreceptor unit provided with a flange with an internal gear. This photoreceptor unit is provided with a reinforcing member in the flange. This photoreceptor unit is provided with a reinforcing member at the flange. Further, this photoreceptor drum rotates upon receiving driving force at the internal gear of the flange via an external gear which serves as a drive gear. Here, the drive gear is smaller in size than the internal gear of the flange. With this structure, the required engagement precision of the internal gear can be maintained.
However, with the structure of the Japanese Unexamined Patent Publication No. 64-21466/1989, even if the drive section and the photoreceptor drum are manufactured with high precision, it would not be possible to completely eliminate eccentric error or axis deviation of gears in engagement, there is no win situation to eliminate such eccentricity or eccentric axis. In this state, when the photoreceptor drum and the drive section are connected without generating jerky movement, for example, due to the excessive force exerted to the connected part, a force is exerted in the direction of disturbing stable engagement of the gears, which hinders smooth rotation movement. Additionally, due to the taper provided at the connected part, a force is exerted in the direction of moving the photoreceptor drum in the axial direction, thereby presenting the problem that deviation of the photoreceptor drum in the axial direction is liable to occur periodically.
According to the structure of Japanese Patent No. 3078464, it is necessary for the driving gear on the side of the image forming apparatus main body. Therefore, a distance between the axes of the external gear and the internal gear is liable to change due to variations in load of the driving transmission, etc., thereby presenting the problem that stable rotation movement of the photoreceptor drum cannot be ensured.